1. Field of the Embodiments
The embodiments are generally directed to chemical detectors and more particularly to an improved chemical detector which fuses previously independent approaches to ion mobility spectrometry (IMS) into a single detector.
2. Description of Related Art
Ion Mobility Spectrometry (IMS) has been the primary technology for chemical warfare agent detection for at least 30 years. Screening of airport passengers for explosives and illegal drugs has relied on IMS for about the same period. There are hundreds of thousands ion mobility spectrometers in use throughout the world. Instrumentation advantages in terms of small size and low electrical power requirements coupled with excellent sensitivity and spectrometric specificity make IMS an ideal technology for field detectors. As with any analytical chemistry technique, improved sensitivity and specificity without sacrificing size, weight, power and cost benefits are continually sought. The number one complaint by users of IMS instrumentation is that the systems are prone to interferences. As requirements for field detection of various and “non-traditional” substances increase, complaints of interferences are likely to increase.
Ion Mobility Spectrometry (IMS) is the study of the motion of gas-phase ions under influence of electric fields. Several methods for study on the ion motion are used throughout the IMS field. A combination or “fusion” of two of these methods is proposed—the IMS methods will be referred to here as “Linear” IMS or just IMS (the traditional term) and “Differential” IMS or DIMS. A detailed treatment of theory and practice of IMS can be found in the book “Ion Mobility Spectrometry—2nd Edition” by G. A. Eiceman and Z. Karpas, CRC Press Taylor & Francis Group, Boca Raton (2005). The substance of this reference is considered to be known to those having skill in the present art and is incorporated herein by reference.
Currently, existing field detectors use either IMS or DIMS, but not both. For example, the LCD 3.3 (Light Weight Chemical Detector) from Smiths Detection uses IMS processing. While the JUNO detector developed by Chemring Detection Systems is exemplary of a previously proposed detector that uses DIMS processing for detection of CWA and low vapor pressure agents.
There is no literature record of IMS and DIMS sensor and data fusion where the two complementary technologies have been operated in parallel. There have been previous attempts to fuse IMS and DIMS technologies as described in E. Nazarov, et al.; “Miniature DMS-IMS Detector for Enhanced Resolving Power;” 16th International Conference on Ion Mobility Spectrometry, Mikkeli, Finland; July 2007 and in A. G. Anderson, et al; “DMS-IMS2, GC-DMS, DMS-MS: DMS hybrid devices combining orthogonal principles of separation for challenging applications;” Chemical, Biological, Radiological, Nuclear, and Explosives (CBRNE) Sensing IX. Edited by A. W. Fountain, P. J Gardner; Proceedings of the SPIE, Volume 6954, pp. 69540H-69540H-12 (2008). The described approach used a DIMS device for rapid separation of target ions and introduction of separated ions into two IMS instruments. A DIMS device separates positive and negative ions simultaneously. Positively charged ions are directed into an IMS device which is appropriately biased and negative ions are directed into the other IMS device. While this design, theoretically, provides for enhanced separation of analyte ions—such is not necessarily the case. Referring to FIG. 3 it can be seen that if the DIMS device selects small ions for analysis by the IMS systems, no resolution is gained since IMS cannot effectively separate small ions. For large ions there is little to no separation by the DIMS system, the IMS system is relied on to separate the ions. In both cases, sensitivity is sacrificed due to ion loses between the mobility spectrometers with insignificant improvements in resolution.